Traveling-wave tube with damping of undesired frequencies

Abstract

A traveling-wave tube has coupled cells in a periodic arrangement defined between apertured irises separated by respective spacers. The spacers have dielectric waveguides terminating in lossly loads to attenuate RF frequencies above the upper limit of the frequency to be amplified by the tube.

We claim: 
     
       1. A traveling-wave tube, comprising: a elongated tube structure having a pair of opposite ends;   an electron gun injecting a beam of electrons into the interior of said structure at one of said ends;   a collector at the other of said ends for collecting electrons traversing the interior of said structure;   a plurality of traveling wave apertured irises spaced periodically along said interior of said structure and defining between them respective cavity cells coupled in succession through said irises, said irises being separated by respective spacers enclosing the respective cells;   means for injecting a radiofrequency signal into said interior of said structure at said one of said ends;   means for extracting an amplified radiofrequency signal from the interior of said structure at said other of said ends;   a magnetic focussing system along said structure;   at least one radially extending dielectric waveguide in each of said spacers respectively coupled to each of said cells and transparent to all frequencies above a prefixed frequency; and   a respective lossy load at an outer end of each of said dielectric waveguides and in contact therewith to dissipate energy of all frequencies passed by the respective dielectric waveguide to the respective lossy load.   
     
     
       2. The traveling-wave tube as defined in claim 1 wherein said dielectric wave guides have cutoff frequencies selected that each waveguide forms a high-pass circuit having as its lower pass frequency, the frequency to be attenuated to prevent oscillation at a higher frequency end of a frequency spectrum to be amplified in said structure. 
     
     
       3. The traveling-wave tube as defined in claim 2 wherein each of said spacers is provided with a plurality of said waveguides and respective lossy loads. 
     
     
       4. The traveling-wave tube as defined in claim 2 wherein said waveguides have a rectangular cross section in a plane perpendicular to an axis of said structure. 
     
     
       5. The traveling-wave tube as defined in claim 2 wherein each of said waveguides and lossy loads is received in recess of the respective spacer. 
     
     
       6. The traveling-wave tube as defined in claim 5 wherein each of said recesses opens along a planar face of the respective spacer. 
     
     
       7. The traveling-wave tube as defined in claim 5 wherein each of said recesses is axially flanked by material of said spacer.